1. Field of the Invention
The present invention relates to a sensor device for detecting moisture of a flowing fluid medium.
2. Description of the Related Art
Numerous sensor devices for detecting at least one property of a flowing fluid medium are known from the related art. The property may basically be any arbitrary physically and/or chemically measurable property which may qualify and/or quantify a flowing fluid medium. In particular, the property may be moisture, in particular humidity, and/or a mass flow and/or a flow velocity and/or a volume flow and/or a pressure, for example an air pressure. The present invention is described below in particular with reference to gas sensors and concentration sensors as described, for example, in Robert Bosch GmbH: Sensoren im Kraftfahrzeug [Automotive Sensors], 2010 Edition, pages 98-101, and/or temperature sensors as described, for example, in Robert Bosch GmbH: Sensoren im Kraftfahrzeug, 2010 Edition, pages 102-111, and/or hot film air mass meters as described, for example, in Robert Bosch GmbH: Sensoren im Kraftfahrzeug, 2010 Edition, pages 146-148. The flowing fluid medium may be a gas or a liquid, for example. The present invention is described below with reference in particular to combustion air and/or exhaust gases of internal combustion engines, for example motor vehicles. However, other applications are also possible in principle.
For example, for more accurate pilot control of an injection quantity and/or for more precise control of exhaust gas recirculation (EGR), it may be necessary to detect the moisture, for example a specific moisture, of drawn-in combustion air. For example, moisture sensors are known from the related art which may be integrated into an air mass meter, or which as a separate sensor may be independently integrated into an intake tract.
Further applications of a sensor device, in particular a moisture sensor, are possible in principle. For example, in low-pressure exhaust gas recirculation (LP-EGR), water vapor may condense in an EGR cooler and/or in a charge air cooler. In particular there may be a risk of corrosion, for example due to acid formation, and/or water impact and/or freezing. In such a system, in each case a bypass is generally provided for an affected cooler, in particular for a charge air cooler, whereby the bypass may be controlled as a function of, among other things, the moisture content, for example the humidity, of the intake air, for example to avoid condensation in a targeted manner.
Capacitive moisture sensors in particular are known from the related art, in which the measuring effect may typically occur due to a change in the electrical capacitance of a hygroscopic polymer. In the process, water molecules typically diffuse into a dielectric as a function of the relative humidity, in particular a relative ambient humidity, and change a capacitance, in particular the electrical capacitance, of the polymer layer due to the high permittivity of water (∈w=80).
German patent application document DE 10 2010 043 083.3 proposes, for example, a sensor device for detecting a flow property of a fluid medium, the sensor device including at least one sensor housing within which at least one pressure sensor and at least one moisture sensor are accommodated. The sensor device may include at least one diaphragm, in particular at least one diaphragm that is at least partially permeable to moisture.
Moisture sensors may be designed as independent sensors or integrated into an air mass sensor. The sensor may include, for example, at least one electronic module and at least one sensor element that is fitted onto at least one plastic frame which has at least one diaphragm that is permeable to water vapor. In addition, the sensor may include at least one fitted-on electronics compartment cover having at least one recess which may allow, for example, a media exchange, in particular an exchange of the flowing fluid medium, with the air in the intake tract.
A sensor for an internal combustion engine, including an air mass meter which has a sensor element for detecting the drawn-in air mass, is known from published European patent document EP 1 017 931 B1. A moisture sensor and a pressure sensor as well as an evaluation circuit for processing the data which are output by the air mass meter or its sensor element, the moisture sensor, and the pressure sensor are provided adjacent to the air mass meter or its sensor element, and situated in a single housing.
The sensor devices known from the related art have several disadvantages. For example, an improvement in the robustness of the sensor device, which in particular includes a moisture sensor, against particle discharge from the flowing fluid medium, in particular a gaseous medium, to be measured would be desirable. Distortion of a measuring signal and/or destruction of the sensor device, for example the sensor, in particular by dust and/or air particles and/or oil and/or water droplets should be avoided. It would be desirable, for example, to protect the moisture sensor, in particular a hygroscopic film which encloses the moisture sensor, from the influence of foreign gases and/or condensation with dirty condensate. This could result in a reversible or irreversible change in a characteristic and/or an ohmic shunt and/or formation of a microclimate and/or corrosion of terminal contacts. Effective protection of the sensor device, in particular the sensor element, may be ensured, for example, by the diaphragm which is permeable to water vapor. For example, water droplets and/or dirty condensate and/or coarse dirt particles may thus be kept away from the sensor device, in particular the sensor element. However, due to solid particles that are entrained in the flowing fluid medium, in particular in the flow, the diaphragm itself may be mechanically damaged and/or filled with dirty condensate in such a way that, for example, water vapor may be hindered or prevented from passing through. In the worst case, a measuring effect may be completely lost, for example due to complete coverage of the surface of the diaphragm with an oil layer. Therefore, a sensor device for detecting at least one property of a flowing fluid medium would be desirable which at least partially suppresses or mitigates the disadvantages of the sensor devices known from the related art.